Opposition MPs in Vanuatu have sent a clear signal that they will use the strength of feeling against the country's membership of the World Trade Organisation as an election issue.

Earlier this week Vanuatu formally became the 156th member of the WTO, after parliament voted last year to support joining.

The formal joining was welcomed by Vanuatu's Ambassador to the European Union and Belgium, Roy Mickey Joy, who said it followed 17 years of protracted negotiations and consultations between Port Vila and Geneva.

But the move has been widely opposed in Vanuatu by churches, unions, chiefs and business leaders, who fear that too many compromises were made to secure membership.

Elections are scheduled in October, and Ralph Regenvanu, an opposition MP, says the issue is expected to feature strongly in opposition campaigns.

"The National Council of Chiefs on behalf of all the chiefs in Vanuatu, the Vanuatu Christian Council on behalf of all the churches in Vanuatu, the Multinational Workers' Union on behalf of workers, the Vanuatu Association of Non-Government Organisations on behalf of NGOs, and even the Chamber of Commerce, on behalf of all businesspeople in Vanuatu, asked the government not to join," he told Radio Australia's Pacific Beat.

Least developed status

Mr Regenvanu says the concern stems from fears that the country will lose some of the rights that Least Developed Country status gives to WTO members.

"No one knows what's in the [membership] package... because when we raised certain questions in parliament, they couldn't be answered," he said.

He said there was uncertainty on whether the country would be free to set tariffs or impose other measures to protect local industries.

However, Astrid Boulekone, general manager of the Vanuatu Chamber of Commerce and Industry, said the chamber was taking a neutral position on WTO membership, and that some members were happy with the decision to join.

But she said there was general dissatisfaction with the amount of consultation with business prior to the parliamentary decision.

"It's almost like the negotiations were conducted at the national level among senior government key officers, and that the private sector was not closely involved in the negotiation process," she said.

Mr Regenvanu says the issue may be contested when Vanuatu holds general elections on October 30.

"We will definitely re-examine the accession process and investigate the possibility for withdrawing from the WTO," he said.

"I understand no country has ever withdrawn, so there may be incredible pressure on Vanuatu, including from Australia - which was one of our working partners for our accession, so Australia has a very strong interest in seeing Vanuatu staying in the WTO.

"Considering all the aid we get, there'll be strong pressure on us not to withdraw. It's going to be raised by people like myself, but we'll see if it becomes an election issue or not."

Free trade is the oldest argument in federal politics and the issue that literally defined the federation era but opposition exists to the TPP, courtesy of the Investor-State Dispute Resolutions clause.